An air preheater and a flue gas NOx reduction (deNOx) reactor are two essential parts of an existing coal-fired boiler, in particular a flue gas treatment device of a coal-fired power station boiler.
The main effect of the air preheater is to use flue gas to preheat air entering the boiler to a certain temperature, thereby recovering heat of the flue gas and reducing the temperature of the flue exhausted from the boiler; and meanwhile, as the air is preheated, the initial temperature of fuel and the air is improved, the ignition and combustion process of the fuel is strengthened, the incomplete combustion loss of the fuel is reduced and the efficiency of the boiler is further improved.
In the aspect of NOx removal of the flue gas, in accordance with regulations stipulated in Emission Standard of Air Pollutants for Thermal Power Plants (GB13223-2011 in China) launched on Jan. 1, 2012, the emission of NOx of all the newly built thermal power units should achieve 100 mg/cm3. Since Jan. 1, 2014, the emission of NOx of all the thermal power units put into operation in key regions has been required to achieve 100 mg/cm3, and the emission of NOx of the units put into operation before 2003 in non-key regions has been required to achieve 200 mg/cm3. The implementation of the new standard has brought great pressure to thermal power enterprises, and the control of nitrogen oxides has also become urgent objective requirement for national economic sustained development and environmental protection. At present, catalytic reduction NOx technology (SCR) has become a flue gas NOx treatment technology which is most widely used in the world, most mature and most effective. According to the technology, ammonia is taken as a reductant and sprayed into the flue for fully mixing with the flue gas and then flows into a reactor loading an SCR catalyst, and under the action of the catalyst, NOx in the flue gas is reduced to harmless nitrogen by the reductant, namely ammonia. At present, the SCR reactor has been widely used in the coal-fired power station boilers.
The air preheater and the SCR deNOx reactor are conventional flue gas treatment devices of the power station boilers, occupying a relatively large space and need relatively high investment and operation cost.